(a) Field of the Invention
The present invention relates to a photosensitive material for use in electrophotography.
(B) Description of the Prior Art
A typical one of the known copying processes in electrophotography is Carlson's process. According to this process, a photosensitive material is first charged with electricity in a dark place and then exposed to light. By this exposure, the photoconductivity of the photoconductor changes, the electric charge of the portion radiated with light leaks to the side of support (to wit, base plate side), and as a result, a latent image corresponding to the difference of the density of charge is formed on the surface of the photosensitive material. Subsequently, this latent image is turned into a visible image by means of a developer (developing powder), and said developing powder is next transferred to a transfer material, such as paper, and is fixed thereon by such means as heating or the like.
To cite the electrophotographic sensitive material known from the outset for use in said Carlson's process, there is one prepared by forming a photoconductive layer on a conductive support. This photosensitive material has thereafter been improved, and a photosensitive material provided with double photoconductive layer, a photosensitive material comprising an insulating layer formed on the photoconductive layer and so forth have been developed with the progress of the electrophotographic process.
However, with the recent marked tendency toward high-speed electrophotographic copying machines, there is a need for improvements of both the sensitivity of photosensitive materials and the durability thereof. For the improvement of the durability of photosensitive materials, it is of course necessary to enhance the mechanical strength of the photoconductive layer per se, but the enchancement of the strength of adhesion between the photoconductive layer and the support is necessary as well. For instance, in the case where the photosensitive material is used in the form of a belt, in order to make the flexibility of photoconductive layer satisfactory, the adhesion between the photoconductive layer and the support must be firm and strong.
From this standpoint, with a view to strengthening the adhesion between the photoconductive layer and the support, there have been proposed various photosensitive materials comprising an intermediate layer (or adhesive layer) consisting of resin formed inbetween the photoconductive layer and the support. For instance, in the specification for U.S. Pat. No. 2,901,348 and Japanese Patent Publication No. 32468/1969 are cited polyvinyl acetal, phenol resin, cellulose lacquer, alkyd resin, polyvinyl carbazole, polyester, polysulfide resin, polyurethane, amino resin, polyvinyl alcohol, silicone resin, polystyrene, chlorinated rubber, epoxide resin, polysulfide silicone resin, polyamide, polysulfide modified epoxide resin, etc. as the resin to constitute said adhesive layer. However, inasmuch as an adhesive layer (or intermediate layer) consisting of such a resin alone would interfere with the leaking of the charge, although it is admittedly effective as the barrier layer of a photosensitive material having a great value of dark decay, in the case of a photosensitive material having a small value of dark decay, it is unsuitable because it will bring about deterioration of sensitivity and will give rise to residual potential.
As a means for eliminating the foregoing defect, it has been proposed to provide an adhesive layer consisting of polyvinyl acetate containing carbon black as the resistance controlling additive inbetween a conductive support and a selenium layer (cf. Japanese Patent Open No. 47631/1975). However, addition of such an additive as carbon black will change the properties of the resin, entailing deterioration of the adhesive property thereof and inferiority of the characteristics of the resulting image owing to the lack of uniformity of dispersion of said additive depending on the mixing ratio thereof, and it will become extremely difficult to determine the conditions for manufacturing a photosensitive material. Besides, the resulting photosensitive material does not come up to the standard intended by the present inventors.